Calculus 1 Questions

1. Let a and b be differentiable.

x^2 x<1

ax+b x> or =1

2. Prove lim as x approaches 3
x^2+x=8

3. A square plot is made at points A,B,C, and D (clockwise). The sides of the square are 100ft long. A pipeline goes from A to a point between B and C and from that point to C. The cost of each side is $20 per ft. and the cost of the pipe inside the square plot is $10 per ft. What is the minimum cost?